Optical vortexes are light beams that travel in helical patterns around their axis of propagation. The electromagnetic waves comprising the beam may cancel each other out at the axis. Thus, the cross-section of an optical vortex beam may resemble a circle of light with a hole aligned at the axis.
An optical vortex is primarily a helical phase ramp accompanied by intensity null and a phase ambiguity at the vortex point. In a plane lateral to the direction of propagation of vortex beam, the wave front undergoes continuous azimuthal phase variation. Such an optical vortex is described by wave field exp(tlφ) where φ is the azimuthal angle and l represents topological charge of the vortex field. The topological charge of the optical vortex is a measure of its helicity. Its magnitude determines the number of cycle of 2π phase change in one revolution about the vortex point and its sign provides information relating direction of phase circulation, clockwise or anticlockwise, of the helical wave. Optical vortices find many applications in a wide variety of fields such as trapping and rotation of micro particles, laser cooling, Quantum data encryption, phase contrast microscopy and image processing.
Some of the devices used for generation of an optical vortex, well known in the prior art, include computer generated hologram (CGH), spiral phase plate (SPP), lithographically etched mirror (LEM) and spatial light modulator (SLM). A major drawback of the devices like CGH, SPP, and LEM is that they can generate vortex with only a fixed topological charge and for a specific wavelength. An SLM can be used for generation of vortex of desired topological charge but its diffraction efficiency is very poor. Moreover, it cannot withstand high optical power which is a prime requirement in certain applications of vortex beams such as optical maneuvering (trapping, rotation and stacking) of micro particles, laser cooling and so on. Segmented and bimorph deformable mirror exhibit flexibility in generation of a vortex and can withstand reasonably large optical power. However, both these devices generate optical vortices, where azimuthal phase variation is not continuous but varies in discrete steps.
Further, the prior art devices cannot be used for any wavelengths or any range of wavelengths for generating optical vortices. The prior art devices are adapted for generating optical vortex only for fixed wavelengths.
The limitations and disadvantages of conventional and traditional approaches of generating optical vortex are apparent to one of skill in the art and hence, there exists a strong need to provide a device for effective generation of optical vortex, at the same time, simple to implement and which overcomes the above mentioned problems. Various embodiments describe a device wherein the above mentioned shortcomings in the generation of optical vortices are taken care of.